As temperatures rose to 28degC yesterday, swimmers were advised against entering bacteria-ridden water at St Clair beach in Dunedin.
The Dunedin City Council monitored bacteria levels daily over summer and closed the beach yesterday because of harmful levels.
According to Otago Daily Times records, it was the first time St Clair had been closed since the beginning of December.
St Kilda was closed once in December but remained open yesterday.
The bacteria comes from sewage from the Lawyers Head outfall pipe, which can flow back towards the shore when certain weather and tidal patterns coincide.
The Tahuna outfall pipe was part of a project to improve the quality of effluent discharged from the Tahuna sewage treatment station and was set to be commissioned next week, council project manager Brian Turner said.
Stage two of the project, which involved upgrading the treatment station itself, was under way.
It was "too early to comment" on when stage two would be completed, he said.
